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We report on the development of a new family of magnetic field sensors with exceptionally low magnetic field noise, as low as 0.3 fT Hz −1/2 . Beside this, they exhibit high usable voltage swings of more than 150 μV pp and tolerable background fields during cool-down of up to 6.5 mT. In operation mode they recover completely from magnetization pulses of up to 76 mT, which makes them well suited for applications such as low-field magnetic resonance imaging.With respect to their easy and reliable use as well as their field resolution in the sub-fT Hz −1/2 range, the presented SQUID sensors are adequate for many applications, such as in geophysics or in biomagnetism.

We study a flux qubit in a coplanar waveguide resonator by measuring transmission through the system. In our system with the flux qubit decoupled galvanically from the resonator, the intermediate coupling regime is achieved. In this regime, dispersive readout is possible with weak back action on the qubit. The detailed theoretical analysis and simulations give good agreement with the experimental data and allow us to make the qubit characterization.

We report on a technology for the fabrication of sub-micrometer sized cross-type Josephson tunnel junctions in niobium technology. We present the fabrication scheme and properties of cross-type junctions with linear dimensions from 10 down to 0.6 µm. Sidewall passivation of the junctions is achieved by anodization as well as by planarizing the junctions with SiO in a self-aligned deposition step. The measured ratio of the sub-gap resistance to the normal resistance is about 35. Because of their low sub-gap current and low parasitic capacitance such junctions are well suited for applications like high resolution SQUIDs.

GaAs-based quantum-cascade lasers based on a bound-to-continuum transition have been realized and characterized. This band structure design combines the advantages of the well known three-well and superlattice active regions. We observed lasing of Fabry–Pérot lasers in pulsed mode up to a temperature of 100 °C. Multimode emission with a pulsed peak power of 340 mW is observed at room temperature and 42 mW at 80 °C. Further, from aging tests we expect a lifetime of over 60 years for these devices.

We have constructed a microwave detector based on the voltage switching of an underdamped Josephson junction, that is positioned at a current antinode of a λ/4 coplanar waveguide resonator. By measuring the switching current and the transmission through a waveguide capacitively coupled to the resonator at different drive frequencies and temperatures we are able to fully characterize the system and assess its detection efficiency and sensitivity. Testing the detector by applying a classical microwave field with the strength of a single photon yielded a sensitivity parameter of 0.5 in qualitative agreement with theoretical calculations.PACS numbers: 07.57. Kp, 74.78.Na, 85.25.Cp The light emission by single, microscopic quantum systems displays a number of non-classical features which have been exploited in fundamental investigations in quantum physics and which may result in applications in metrology, quantum communication and computing. Potential applications, however, would suffer from the rather weak coupling between atoms and single optical photons. This has stimulated efforts to study the same features with macroscopic artificial atoms. A particularly successful system relies on solid state superconducting circuits. Due to the Josephson non-linearity such circuits have an anharmonic excitation spectrum and may be restricted to an effective two-level systems which can interact resonantly with microwave fields. Besides the stronger coupling of superconducting circuits, an additional advantage is that they can be designed and fabricated on chip-scale, thereby allowing the integration in and scaling to larger systems with multiple components.Essential quantum optical effects with superconducting qubits, such as vacuum Rabi splitting [1], resonance fluorescence of a single artificial atom [2], and single atom lasing [3] have already been observed. Microwave fields can be amplified, detected and fully characterized in homodyne set-ups [4]. The effective coupling to transmission wave guides has made it possible to efficiently monitor the emitted radiation and verify the validity of the quantum trajectories of qubits conditioned on the detection record [5,6], as well as to apply feedback and stabilize coherent superposition states of the qubit [7].Quantum optics benefits from high efficiency single photon detectors. It relies on the energy of the individual photons being sufficient to exploit the photoelectric effect and liberate an electron which can be amplified and detected [8]. Transition edge sensors [9] and superconducting nanowire single photon detectors [10,11] also require a sufficiently large energy of the incident photon to heat and thus modify the current through the detector. The energy of microwave photons is too low to allow detection by these methods, and for this energy range both controllable single photon sources and efficient single photon detectors are still under development.When working in the single photon regime, it is an obvious choice to use the resonant coupling to qubit systems. Indeed...

We describe a method for charging atomic vapor cells with cesium and buffer gas. By this, it is possible to adjust the buffer gas pressure in the cells with good accuracy. Furthermore, we present a new design of microfabricated vapor cell arrays, which combine silicon wafer based microfabrication and ultrasonic machining to achieve the arrays of thermally separated cells with 50 mm(3) volume. With cells fabricated in the outlined way, intrinsic magnetic field sensitivities down to 300 fT∕Hz(1∕2) are reached.

Superconducting NbN x thin films were deposited by plasma-enhanced atomic layer deposition (PEALD) using the metal organic precursor (tert-butylimido)-tris (diethylamino)-niobium (TBTDEN) and hydrogen plasma. The transition temperature T C and the resistivity of the NbN thin films were measured by four-point probe measurement. Their composition was analyzed by x-ray diffraction and Rutherford backscattering spectroscopy. The deposition process was optimized to obtain a low resistivity as well as a high superconducting transition temperature. A T C close to 10 K and a resistivity of 2.5 µ m as well as a critical current density of 8.9 × 10 5 A cm −2 were achieved. Originally, a high oxygen concentration was detected in the compound. By variation of the plasma parameters, the concentration could be reduced from 57 atom (at.)% to 11 at.%. Because of the excellent thickness control and conformality, such ALD films may be suited very well for applications in superconductor electronics and sensing devices.